Binder for explosive compositions



United States Patent BINDER FOR EXPLOSIVE COMPQSITIONS William G. Finnegan, Rex L. Smith, and Armin T.

Wiebke, China Lake, Calii, assignors to the United States of America as represented by the Secretary of the Navy No Drawing. Filed Get. 16, 1958, Ser. No. 767,753

3 Claims. (Cl. 149-19) (Granted under Title 35, [1.3. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention is directed to an explosive-containing composition for coating electric bridge wires, graphite bridges and other initiating devices, and to a squib incorporating the thus coated initiating device.

Prior methods of binding explosive compositions to initiating device involved the use of binding materials such as nitrostarch, nitrocellulose, and certain naturally occurring gums. Both nitrostarch and nitrocellulose deteriorate with age, however, liberating harmful gases and losing their qualities as binders. Furthermore, nitrostarch is brittle and does not form good films, while nitrocellulose is known to inhibit or delay the ignition of the explosive compositions used.

The natural gums are subject to the disadvantages of being water soluble, relatively poor adhesives, and they may also inhibit or delay the ignition of the explosive compositions used with them as nitrocellulose does.

It is therefore an object of this invention to produce a composition for binding explosive compositions to initiat in'g devices in which the binding agent will not deteriorate with age.

Another object is to provide a composition of the type aforementioned in which the binding agent is not watersoluble.

A further object is to provide a composition of the type aforementioned in which the binding agent will not inhibit or delay the ignition of the explosive.

Still another object is to provide a composition of the aforementioned type in which the binding agent has all the aforementioned qualities and in addition has the quality of being compatible with commonly used solid initiating explosives.

A final object is to provide a squib utilizing the aforementioned compositions which has a longer storage life and is more reliable than previous squibs.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following detailed description.

The aforementioned objects are accomplished by a mixture of a suitable explosive composition in a binder of polymeric Z-methyl-5-vinyltetrazole. The mixture is coated upon an initiating device which is then assembled into a squib.

A wide variety of primary or initiating explosives have been used in connection with squibs in the past. Such explosives include tetrazene, lead styphnate, both normal and baisc, diazodinitrophenol, lead mononitroresorcinate, ammonium perchlorate, and numerous metal-oxidizer mixtures. lMost metals, when burned to their oxides, will release large quantities of heat and most of them will release it rapidly enough to heat any gaseous reaction-products and surrounding air to the point of becoming explosive. Aluminum, magnesium, boron, and zirconium are the metals commonly employed however. Likewise many oxidizing agents are operative but those commonly employed are nitrates, chlorates, perchlorates, and certain oxides.

The particular binder, poly-2-methyl-5-vinyltetrazole,

3,655,780 Patented Sept. 2'5, 1 96 2 used in the instant case in combination with any of the prior art explosive compositions, is a high molecular weight, nitrogen-containing material which has a heat of explosion of about 410 calories per gram evolved.

The amount of binder used may vary from as little as weight percent to as high as 25 weight percent. Of special interest is the range of about /2 percent to two percent. No more than that necessary to bind the explosive together should be used, however, since it is desirable to have as much explosive present as possible.

Poly-2-methyl-S-vinyltetrazole is made as follows: A mixture of 213 g. (3.0 moles) of hydracrylonitrile,.214.8 g. (3.3 moles) of sodium azide, 176.7 g. (3.3 moles) of ammonium chloride and 1500 ml. of dimethylformamide is heated at 123127 C. with stirring for 25 hours. The dimethylformamide is then removed at 100 C. under reduced pressure (ca. 20 mm.). Care should be taken to remove the dimethylformamide in this operation as completely as possible. The residue of sodium chloride and S-hydroxyethyltetrazole is then dissolved in 250 ml. of water and made basic With a solution of 140 g. (3.5 moles) of sodium hydroxide in 250 ml. of water. The temperature should be maintained at ca. 25 C. during this step to prevent excessive foaming. The solution is then stripped to about half volume at reduced pressure on a steam bath. The pH of the solution at this time should be 9 or higher. If the pH is lower than 9,.additional base should be added and the evaporation con tinued until the pH remains at 9 or higher. The solution is then cooled to room temperature and acidified to about pH 2 with 300 ml. of concentrated hydrochloric acid (or more if additional base had been used). It is advantageous at this point to cool the solution to 5 C. and remove the precipitated sodium chloride by. filtration. The filter cake is washed with ethanol and the filtrate combined with the product solution. The acidified product solution and alcohol washings are then stripped of solvents at C. under reduced pressure. The 5- hydroxyethyltetrazole is then extracted from the residue with one 500 ml., one 250 ml. and one m1. portions of cold 95% ethanol and neutralized to a phenolphthalein endpoint by the addition of a solution of 197.4 g. (3.0 moles) of 85% potassium hydroxide in 625 ml. of 95 ethanol with stirring and cooling. 7

The 3.0 moles of potassium S-hydroxyethyltetrazole in 1500 ml. of 95% ethanol from the previous reaction is placed in a 3 liter, 3 necked flask.

Potassium bicarbonate (30 g., 0.3 mole) is added and 417 g. (3.3 moles) of dimethyl sulfate is added dropwise with stirring over a 30 minute period. The temperature of the solution is maintained at 2833 C. during the addition and for an additional 30 minutes and then raised to 40-45 C. for 30 minutes. The solution is then cooled to 5 C. The precipitate of potassium methylsulfate is removed by filtration and the filter cake is washed with several portions of 95% ethanol. The combined ethanol filtrates are evaporated to dryness at reduced pressure on a steam bath.

The 1- and 2-methyl-5-(Z-hydroxyethyl)tetrazoles are extracted from the residue with a total of 350 ml. of chloroform and the chloroform solution is dried for one hour with magnesium sulfate, or alternatively by azeotropic distillation of part of the chloroform. (If the vacuum stripping of the ethanol and water in the previous step is thorough, the chloroform solution should be essentially dry. Care should be taken that the chloroform solution is dry before the chlorination reaction.)

The solution of 1- and 2-rnethyl-5-(2-hydroxyethyl)tetrazoles in 350 ml. of chloroform from the preceding methylation reaction is cooled to 5 C. and 300 ml., 537. g. (4.5 moles) of thionyl chloride is added with stirring at a rate such that the reaction temperature does not rise above 25 C. The solution is then heated to reflux for four hours, or longer if necessary, to complete the evolution of hydrochloric acid and sulfur dioxide. The chloroform and excess thionyl chloride are then removed at reduced pressure on a steam bath. The heating at reduced pressure should be thorough to ensure complete removal of any thionyl chloride, but it is also essential that there be excess thionyl chloride at the end of the reflux period. The residue of products is then cooled to room temperature and dissolved in 300 ml. of chloroform. Water (200 ml.) is added and the mixture is stirred and cooled to 5 C. Solid sodium bicarbonate is then added, with stirring and cooling in suflicient quantity (0.2-0.3 mole/ mole) to bring the pH of the mixture to 6-7. The chloroform layer is then separated and the water layer is extracted with an additional 100 ml. portion of chloroform. The combined chloroform solutions are dried with magnesium sulfate and stripped to dryness at reduced pressure on a steam bath. The residue of mixed 1- and 2-methyl-5-(2- chloroethyDtetrazoles is then heated to 100 C. at 10-20 mm. pressure and stripped of the low boiling impurities present. 2-methyl-5-(2-chloroethyl)tetrazole is then removed from the mixture of chloro compounds by high vacuum distillation.

The 2-methyl-5-(2-chloroethyl) tetrazole from the preceding reaction is dissolved in 250 ml. of methanol and the solution is heated to reflux. A solution of approximately 98.5 g. (1.5 moles) of 85% potassium hydroxide in 500 ml. of methanol is then added dropwise with stirring over a period of one hour and the reaction is stirred and refluxed for an additional hour. The solution is then cooled to room temperature, neutralized to pH 6-7 with concentrated hydrochloric acid and one gram of hydroquinone is added. The methanol is removed by distillation at atmospheric pressure on a steam bath. The residue of salts and products is cooled to room temperature and the products are extracted with one 0 ml. and two 50 ml. portions of methylene chloride. The methylene chloride solution is dried with magnesium sulfate and the solvent is removed by distillation at atmospheric pressure on a steam bath. The 2-methyl-5-vinyltetrazole is removed from the mixture of crude products by distillation at mm. pressure; B.P. ca. 80 C., N -1.4800.

Emulsion polymerization of this monomer was accomplished as follows: 1 1 g. (0.1 mole) of Z-methyl-S-vinyltetrazole was added with stirring to a solution of 15 drops of sorbitan trioleate in 80 ml. of distilled water. Nitrogen was bubbled through the water during the formation of the emulsion and the duration of the polymerization. The emulsion was cooled to 02 C. in an ice bath. One ml. of a solution of 0.03 g. of ferrous sulfate heptahydrate in 100 ml. of distilled water was added, followed by 0.025 g. of ammonium persulfate and 0.025 g. of sodium metabisulfite. The temperature was maintained at 12 C. After 24 hours, the conversion to polymer was estimated at 50% and after 46 hours the conversion appeared reasonably complete, although some odor of monomer was still present. The polymer was a solid rubbery mass at this point. The product was kneaded under distilled water until free of soap and inorganic salts, cut into small pieces and dried. The dried polymer was dissolved in 250 ml. of ethylene dichloride and precipitated into 500 ml. of cyclohexane. The polymer was removed by filtration and dried. Intrinsic viscosities in chloroform at 25 C. for polymers from various batches prepared as above varied from 3.910 to 4.232 depending upon the batch.

Bulk polymerization of 2-methyl-5-vinyltetrazole was effected by the use of benzoyl peroxide or azobisisobutyronitrile as the catalyst. Intrinsic viscosities in chloroform at 25 C. for the polymer prepared by this method varied from 1.055 (60 C., 1 mole percent azobisisobutyronitrile) to 3.812 (40 C., 0.1 mole percent azobisisobutyronitrile). One polymer, from a bulk polymerization run for 48 hours at 50 C. (0.1 mole percent azobisisobutyronitrile), had an intrinsic viscosity in chloroform at 25 C. of 5.606. Precipitated poly 2-methyl-5-vinyltetrazole (purified polymer from a bulk polymerization run for five days at 40 C., 0.1 mole percent azobisisobutyronitrile) was vacuum pressed into pellets at 110 C. and 3000 p.s.i. The pellets are well consolidated and semitranslucent. Molecular weights estimated from intrinsic viscosity data varied in a range from 500,000 to several million.

In Table I which follows, there is presented a number of specific formulations in weight percent which were found to be highly effective as initiating compositions for bridge wires.

Table I Explosive Wt. Binder (Poly-2-methy1-5- percent percent vinyltetrazole) 1. Diazodinitrophenol 75 5 Excess.

Potassium chlorate 25 2. Lead styphnate 75 25 3, Basic lead styphnate... 5 4. Tetraeene 1 Do. 5. Lead mononitroresorcinate.. 98 2 6. Ni(NHs)4[C(NOz)a]2 100 0. 5 D0. 7. C0(NH3)5(N3)3 100 0.5 D0. 1 D0. 2 Do. 8. Zirconium 19. 5 1 D0.

Lead styphnate 35 Lead dioxide 45. 5 10. Potassium Perchlorate 65. 7 2 Do. Aluminum 34. 3 1 Do. 0.5 Do. 11. Potassium Perchlorate 58.7 2 D0.

Magnesium 41. 3 12. Potassium Perchlorate 82.8 2 Do.

Boron 17. 2 13. Zirconium 25 2 Do.

Lead dioxide 75 The coating compositions of this invention are made by placing the finely divided explosive material in a vessel and adding a solution of the binder dissolved in 1,1,2-trichloroethane, some other chlorinated hydrocarbon, or another suitable solvent, such as acetonitrile until the desired amount of binder is present, then adding more pure solvent with mixing until a very thick slurry results.

The bridge wire is coated by simply spreading the slurry, which is practically a paste, upon the bridge wire and drying at room temperature for several hours, whereby the solvent evaporates leaving a coating of the composition upon the wire.

The squib is made, for example, by inserting the bridge wire plug, which has two terminals with a small w-ire between and leads leading from the two terminals, into a closed tube usually containing a layer of black powder at the bottom and a layer of explosive material on top of the black powder, so that the plug is in contact with the explosive. When an electric current of enough magnitude passes through the bridge wire, the resulting heat ignites the coating.

The compositions listed in Table I were prepared and coated on bridge wires and the squibs assembled. The squibs were then tested by sending 1.5 amperes of electricity at 6 volts through the bridge wires which were from 1 to 2 mils in diameter. Ignition occurred in all cases with acceptable delays.

By comparison, the nickel and cobalt complexes using nitrocellulose and polymethylmethacrylate as binders instead of poly Z-methyl-5-vinyl-tetrazole with butyl acetate as the solvent failed to ignite when subjected to 1.5 amperes current at 6 volts potential.

The nickel complex is prepared by taking 5 ml. of a 0.5 M solution of Ni(NO and diluting it with water to 40 ml.; then 3.0 grams of HO(NO is added. 5 M NH solution is added in small increments and a precipitate forms; addition of NH increments is continued until no more precipitate forms. The precipitate is removed by filtration and washed with two 25 m1. portions of 95% ethanol followed by washings with three 25 ml. portions of diethyl ether. Then the precipitate is dried for three hours at 75 C. The yield of yellow-green 3)4] a)3]2 is 3.5 g.

The squibs made according to this specification have been successfully tested in propellant grain ignition. The squibs were positioned in an igniter which was positioned in the perforation in a rocket propellent grain. Very smooth ignition resulted in all cases, at pressures of both 760 mm. and mm. of Hg.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A composition of matter consisting essentially of about 0.5 to 25 weight percent poly 2methyl-5-vinyltetrazole and about 75 to 99.5 weight percent of a material selected from the class consisting of tetrazene, normal lead styphnate, basic lead styphnate, diazodinitrophenol and potassium perchlorate in about 75 to 25 ratio, lead mononitroresorcinate,

a mixture of zirconium, lead styphnate and lead dioxide in weight percents of about 20 to to 45, respectively, a mixture of about 35 weight percent aluminum and the remainder an oxidizing agent from the class consisting of potassium perchlorate, potassium nitrate and potassium chlorate; a mixture of about 41 weight percent of magnesium and the remainder an oxidizing agent from the class consisting of potassium perchlorate, potassium nitrate and potassium chlorate; about 17 weight percent of boron and the remainder an oxidizing agent from the class consisting of potassium perchlorate, potassium nitrate and potassium chlorate; and a mixture of about 25 weight percent of zirconium and the remainder lead dioxide.

2. The composition of claim 1 which contains about 0.5 to 2% poly-2-methyl-S-vinyltetrazole and the remainder Ni(NH [C(No 3. The composition of claim 1 which contains about 0.5 .to 2% polymer and the remainder Co( NH (N Zenftman July 4, 1950 Zebree Jan. 6, 1953 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF ABOUT 0.5 TO 25 WEIGHT PERCENT POLY 2-METHYL-5-VINYLTETRAZOLE AND ABOUT 75 TO 99.5 WEIGHT PERCENT OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OF TETRAZENE, NORMAL LEAD STYPHNATAE, BASIC LEAD STYPHNATE, DIAZODINITROPHENOL AND POTASSIUM PERCHLORATE IN ABOUT 75 TO 25 RATIO, LEAD MONOITRORESORCINATE, 